Business and consumers use a wide array of wireless devices, including cell phones, wireless local area network (LAN) cards, global positioning system (GPS) devices, electronic organizers equipped with wireless modems, and the like. The increased demand for wireless communication devices has created a corresponding demand for technical improvements to such devices. Generally speaking, wireless system designers attempt to minimize the cost of conventional radio receivers while improving the performance of such devices. Performance improvements include, among other things, lower power consumption, greater range, increased receiver sensitivity, lower bit error rates (BER), higher transmission rates, and the like.
A mobile station (or wireless device) routinely performs a cell search (or synchronization) function to detect and acquire the base stations of a wireless network in the vicinity of the wireless device. Fast detection of the base stations is critical to the performance of both the mobile station and the wireless network, particularly in the new 3GPP wideband code division multiple access (WCDMA) wireless systems currently under development. Fast detection of base stations allows a mobile station to access a wireless network more rapidly (i.e., reduces acquisition delay). Fast detection of base stations also enables the mobile station and the wireless network to perform faster handoffs between base station cell sites or between sectors of the same base transceiver subsystem (BTS) of a base station. Additionally, fast detection reduces the number of calls that are dropped during the handoff process.
However, the speed with which conventional mobile stations perform cell searches in 3rd Generation Partnership Project (3GPP) WCDMA networks is relatively limited due to the complexity of the signal processing involved. A conventional mobile station typically performs three search stages in sequence. First, a primary search stage detects slot boundaries in the pilot channel signals of the wireless network. Next, a secondary search stage detects frame boundaries of the pilot channel signals. Finally, a tertiary (third) search stage detects the Gold codes for the base station. When all three stages are complete, a reset signal resets the three search stages and the process repeats. If noise or multipath fading causes the signal to be received improperly, the cell search process cannot resume until all three stages are complete and the next reset signal occurs. This reduces the speed and efficiency of the cell search process.
The speed of acquisition is also reduced by false lock conditions. One of the main goals in designing the cell-search module is to reduce the false lock probability at the final stage. False lock of the searcher, namely the condition in which the third stage of the process locks to an incorrect base station and/or frame timing, results in further delays during post-processing of the erroneous acquired timing/code. This delay, apart from being intolerable for the user, reduces the battery life of the mobile terminal.
Therefore, there is a need in the art for improved wireless mobile station receivers. In particular, there is a need for improved apparatuses and methods for performing synchronization functions (or cell searches). More particularly, there is a need for wireless receivers that can more rapidly search for and acquire the base stations of a wireless network cell site, with a reduced number of false lock conditions.